I see a lot of talk of silvia brakes on 1200 struts. Seemed like a good conversion to me at first BUT.....

A mate asked me to machine his hubs to fit inside the silvia disc

I thought no worries, but looking at how much material and where it needs to be removed the engineer in me got very concerned

I do no think this is a SAFE conversion at all, you need to remove around 50% of the material in the most highly stressed area of the hub. Add to that the fact you are putting them usually on a more highly powered car with much grippier tyres and going much faster than intended by the manufacturer would have designed for - this to me is a recipe for disaster

Yes, i know some guys on here have track cars using this conversion, and if they modified the hub this way i honestly think they are ticking time bombs

I have a mechanical engineering background and have showed a couple of engineer friends, they all cringe

To have a front hub fail is probably the scariest failure of them all especially at 100kmh plus

So please consider this warning if doing this conversion or if you have already done this on your car. The decision is then up to you

I just feel obliged to warn people who may not understand the effect the machining has on the strength of the hub

What about using 1200 (B110) drum hubs on the 1200 disc struts - they will require no machining. Only a 5mm difference in offset using thicker caliper bracket or a 5mm spacer.

not sure about 1200 struts, but i used aussie 120y struts on my ute
didnt take much off at all to fit the discs over them, barely gave them a tickle

its a great conversion if you ask me, i had good results on both street & track

i heard it's only 1mm machined off

I thought it would be easier to take a little off the rotor?

you could, but if you take it off the hub then your discs will fit off the shelf
which is a plus for those without easy access to a lathe

sounds like perhaps the 1200 hubs need more taken off than 120y's though from what rc is saying

I just had another look at the pic. Looks like the outer diameter of the hub (beyond the studs)has to be reduced and the centre bore of the rotor has to be enlarged. I cant see how this would make the hub weaker?

perhaps there is different combo's. the ones i had needed the hubs machined down up to 5mm, definitely not just 1mm

I was considering opening the disc as well as machining down the hub, but with the parts i had it looked like a bad idea

The concern would be cracking the hub between the stud hole and outer OD

I agree 1mm would be fine

once the wheel is tightened down, it's tight. So the loading is #OOPS# all.
5mm is sweet FA.
I showed my S13 conversion to mu local modified vehicle certification engineer. He said it looked fine to him. Then he called his son over, and recommended he do the same swap on his 120Y.
Once sh1t is pulled up tight, there is fVck all hub splitting force on the hub.

don't get me wrong, i'm not claiming to be a know it all or anything, just concerned for fellow members safety/cars

your statements annoy me to be honest, 5mm is not FA if you only have 10. I am concerned about fatigue not "splitting force?". Being "pulled up tight" does not mean there is no longer force on the hub or studs. All tyre/wheel forces are transmitted through the wheel stubs to the hub and therefore to the suspension

To be honest i am surprised an engineer would pass a 1200 with upgraded wheel size and engine power through standard size wheel bearings, as they are my other concern with this setup... you are still using a very small wheel bearing. This is ok if you have a frequent strict replacement policy, though i suspect no one does that. On the other hand i'm not that suprised this would be overlooked by the engineer though (they usually only take this into account if you are going larger than 14" wheels in aus anyway).

But to re-iterate - I'm not telling people what to do, just informing people what risk they may be taking. At the end of the day i hurtle my rally car between gum trees on weekends and am happy i understand the risk involved so i'm happy doing so